CITY Councilman Eric Gioia has gone “carbon neutral.” For his birthday fund-raiser last night at the W Hotel in Times Square (selected for its proximity to so many subways), there were no paper invites. Plus no bottled water was served, only tap, to such guests as Morgan (“Supersize Me”) Spurlock, who was Gioia’s NYU roommate. Karenna Gore Schiff was slated to introduce the council member, who vowed to plant trees to offset all the hot air the event generated. Goia hadn’t specified yesterday exactly how many trees that would take.